Measuring Concentration of Ice Nucleating Particles in the Atmosphere, Particulate Matters and Gaseous Pollutants in Museums: Insight from Models and Elemental Analysis.
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Date
2017-10
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Addis Ababa University
Abstract
Ice nucleation in clouds affects the optical thickness and lifetime of mixed-phase
clouds and is responsible for a significant proportion of precipitation formed globally
and ultimately indirectly affect climate. In mixed-phase clouds, where temperatures
range from −370C and 00C, ice crystals can only form on certain aerosol particles.
Ice nucleating particles (INPs) constitute such aerosols with reduce energy barrier
of ice nucleation. Despite significant advancement in the fundamental understanding
of different ice formation processes in the last decades, the ice phase in clouds
still contributes major uncertainties in climate model prediction of radiative forcing.
This is partly due to a limited understanding of the behaviour of aerosol particles
to act as INPs and paucity of observational data in the atmosphere quantifying INP
distributions. Therefore, the first part of this employed Micro-liter Nucleation by Immersed
Particle Instrument (μ-NIPI) to cool down droplets containing ice-nucleating
material at a controlled rate and to monitor their freezing temperatures. The experiments
reveal that aerosol droplets started to freeze at −140C down to -250C;while,
the concentration evolved from 0.1 to 10−3 cm−3. The average temperature in which
50% of the droplets froze occurred at −200C with a concentration of 10−3 cm−3. The
experimnets have shown that the type of aerosol species that make INPs in Leeds,
UK, were dominantly feldspar from mineral dust. Moreover, meteorological factors
such as wind speed, temperature and relative humidity affected INPs’ concentrations.
In addition to the aforementioned aerosol radiative forcing (climate forcing), aerosol
has significant impact on the environment (e.g., air and water pollution). In fact, pollution
is not a phenomenon just of modern time; it is intimately connected with the
xiv
dawn of the industrial age in which the effects of particulate matter and gaseous pollutants
on precious cultural assets become obvious. The high atmospheric load caused
strong soiling as well as corrosion outdoors and indoors. The increasing attraction
on indoor pollutants in the museums environment and associated investigation contribute
to the understanding of basic mechanisms. Particulate matter and gaseous
pollutants are involved in deterioration processes and aging mechanism was not realized
until macroscopic observable damages occurred which gave the starting point for
scientific investigation. Therefore, in the second part of this work, particulate matter
samples were collected on Teflon membrane filters using Harvard-type Impactor collector,
Aethalometry and diffusive sampler are to measure black carbon and gaseous
pollutants respectively. It was observed that the daily PM10 average mass concentrations
inside and outside the Magritte and Reserve OB museums-varied between
2.71 and 5.25 μg/m3 with an average concentration of 4.10 μg/m3 and 0.36 and
7.75 μg/m3 with an average concentration of 2.20 μg/m3 respectively. The concentrations
were usually lower when the museum was closed and there were no tourist
activities around. Inside the museums, mass concentrations were much less than
outside with daily variations, which were due to wind speed, wind direction, human
activity and traffic activities outside of the museums. The average mass concentrations
of indoor PMs were always lower than that of the outdoor ones that as reflected
in low indoor/outdoor ratios indicating that the sources of pollutants were from outside
the museums. Particle number concentrations in all sizes (i.e., PM1, PM2.5 and
PM10) remained at high levels during morning time which are correlated directly with
temperature and inversely with relative humidity. Furthermore, the concentrations
of gaseous pollutants (NO2, SO2 and O3) were lower inside the museums than the
outside with some of them at undetectable levels; in addition, the levels of these gases
inside the two museums were lower and below the recommended level when compared
to that of other museums. Bulk aerosol samples of different sizes were analyzed by
means of energy-dispersive X-ray fluorescence analysis (EDXRF) to determine their
composition. The analysis led to identification of 11 elements (Al, Si, P, S, Cl, K, Ca,
xv
Mn, Fe, Cu and Zn). The levels of concentrations of these elements were found to
be 27.45 and 281.85 ng/m3 at Magritte and 16.16 and 154.26 ng/m3 at Reserve OB
inside and outside of the museums on average respectively; their sources were predominantly
anthropogenic from traffic activities and industries. It was observed that
air mass with trajectories emanating from maritime and continental sources severely
affected the concentrations pollutants in the museums
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Keywords
Measuring Concentration of Ice Nucleating